In an automobile engine, the rotation of a crankshaft is transmitted to camshafts by means of a timing chain made of iron (hereinafter, simply referred to as a “chain”) so as to rotate the camshafts, thereby opening and closing valves of combustion chambers.
Chain transmission devices are used to drive such camshafts. Many of such chain transmission devices include a crank sprocket attached to a crankshaft of an engine, cam sprockets attached to respective camshafts of the engine, a chain trained around the crank sprocket and the cam sprockets, a loose side chain guide arranged so as to guide the portion of the chain configured to move from the crank sprocket toward one of the cam sprockets, and a tension side chain guide arranged so as to guide the portion of the chain configured to move from the other of the cam sprockets toward the crank sprocket.
As the loose side and tension side chain guides used in such chain transmission devices, sliding-type chain guides are known each having a guiding surface extending along the direction in which the chain moves, and coming into sliding contact with the chain. However, since such sliding-type chain guides are in sliding contact with the chain, there is the problem that the resistance to the movement of the chain is large so that the transmission loss of torque is large.
In order to overcome this problem, the inventors of the present application have proposed a chain guide including a plurality of rollers arranged along the direction in which the chain moves while being spaced apart from each other, and configured to guide a chain (see PCT International Publication No. 2010/090139 and Japanese Unexamined Patent Application Publication No. 2013-032826).
Since this chain guide is in rolling contact with the chain, there is the advantage that the resistance of the movement of the chain is small so that the transmission loss of torque is small.